This invention relates to the diffusion transfer process and, more particularly, to a silver halide photosensitive material for use in said process.
The principle of silver complex diffusion transfer process (referred to as DTR process) is disclosed in U.S. Pat. No. 2,352,014 and is well known. In the DTR process, a silver halide is imagewise transferred, by diffusion, from a silver halide emulsion layer to an image receptive layer and converted therein to a silver image in the presence of physical development nuclei in most cases. For this purpose, the imagewise exposed silver halide emulsion layer is disposed in contact with or brought into contact with an image receptive layer in the presence of a developing agent and a silver halide complexing agent so that the unexposed silver halide may be converted into a soluble silver complex; the silver halide in exposed areas of the silver halide emulsion layer is developed into silver (chemical development) and, as a consequence, becomes insoluble and nondiffusible. The soluble silver complex formed from the silver halide in unexposed areas of the silver halide emulsion layer is transferred to an image receptive layer wherein it is developed generally in the presence of development nuclei; in the case of a direct positive silver halide emulsion, such behaviors of silver halide become reversed in both the exposed and unexposed areas.
In the DTR process which operates in the above-mentioned manner, the quality of the finished image receptive material such as, for example, the density, tone, and contrast of the image and the storage stability of the resulting reproduced image becomes important. Although, in some cases, a continuous tone original is reproduced on the image receptive material, yet a higher contrast, sharpness, and resolution are required when the finished image recptive material is used in the reproduction of books and printed documents or as block copy for printing plate making.
Even though a photosensitive material, image receptive material, and processing solutions are designed to reproduce an excellent image, it is impossible to achieve the intended result, if there occurs slipping between said materials which must remain in tight contact with the coated sides facing each other during the development. It is readily conceivable that the slipping which takes place between two materials has something to do with the tackiness of the coating layer. In fact, the slippage becomes enhanced when the developer contains a thickening agent such as carboxymethylcellulose, hydroxyethylcellulose, or the like. It is a common practice to incorporate a matting agent to roughen the surface of a photosensitive material in order to keep a photosensitive material from becoming tacky or adherent and to prevent the accumulation of static charge. The slipping between the two materials in tight contact can thus be prevented by the incorporation of a matting agent in the surface layer.
Now, the present inventors confirmed that in the silver image areas formed on an image receptive material, there exist tiny spots of pin-point size which are devoid of silver (such tiny spots are referred to as pinholes) and that even if such pinholes are so tiny that they do not impair the practical quality of reflection image, yet they become conspicuous in number in the case of transparency image such as that formed on a transparent film support. Such pinholes seem, by inference based on the result, to be caused by the locally hindered diffusion of the silver complex from the photosensitive material to the image receptive layer. Although the exact cause for the emergence of pinholes is not yet fully elucidated, the present inventors have succeeded in ascertaining that one of the important factors is the presence of a matting agent in the surface layer of photosensitive materials.